Improvements of air quality in large urban areas

Large urban areas like Sao Paulo and Mexico City suffer from air quality problems as a consequence of poor cleaning techniques for gaseous efluents. SOx, NOx and pariculates come mainly from the intensive use of surface public transportation and industrial plants with poor pollution control facilities. The question represents an health hazard mainly in the winter when thermal inversion occurs. The proposal for the reduction of small particles coming from buses flue gas is the use of tubular electrostatic precipitators at the exaust pipe of the vehicle. This is an old and well known technique already tested expeimentally many years ago and shown to the public through educative films. The only problem at the moment is the political will to implement the idea.Hazardous gases can be also be collected by adsorption in activated carbon.Recovery of the carbon can be done by burning since most gases are flamable organic substances. Bsg filters can be used to retain small particles. Purchasing and maitenance costs ate low but there is a limitation on the temperature of the process since the cloth can burn.For larger particles the settling gravitational chamber is a cheap solution. The absence of movable parts leads to low construction and maitenance costs.For medium size particles (10 to 20 microns) the cyclone is recommended. The conclusion is that air polution control in large urban areas is viable and it should be done to improve the quelity of life in these places.